meat and blood change in content and thus scent and flavor when an animal knows it is dying. This is why, when hunting, you do not want the prey to know it's coming, nor do you want to have to take more than one shot to end its life.
Cortisol is undesireable.
https://www.nature.com/articles/34045
Published: 01 January 1998
The physiology of the hunted deer
Hunted (by hounds) deer also had levels of cortisol 70 times those of shot (by rifle, unaware) animals, along with tenfold increases in both haem, the pigment released by damaged red blood cells, and two enzymes ordinarily at high levels only in striated muscle: creatine kinase and a form of lactate dehydrogenase.